Mr. Jr. E. 8. Monck—Date of the Ice Age. 523 



"When in the mine alone and all work is suspended, I have frequently 

 heard strange and unearthly (?) sounds, such as rattlings, seratchings, 

 knockings, etc. — noises called " nackings " by the men. In York- 

 shire 1 have heard of bumps of such magnitude taking place as to 

 throw down large areas of roof in worked-out parts of the pit, and 

 ■which created a blast in the air of the mine strong enough to knock 

 men over, upset tubs, blow open doors, put out lights, and cause 

 much havoc. 



Subterranean rumblings, as is well known, have for several years 

 been heard, and felt too, beneath and in the vicinity of the town of 

 Sunderland ; but these are considered to be due, not to coal-mining, 

 but to the dissolution of the magnesian limestone by water which is 

 constantly being pumped through it. 



Now, it appears to me, that there is one common cause for all 

 these " explosions," " bumps," " nackings," etc., which is simply this : 

 the upsetting, by the excavation, of the equilibrium of the strains or 

 pressures holding everything fast and firmly together — the removal 

 of the support thereby causing the rocks to get relief and to fly off 

 or apparently to explode. I look upon the phenomena as miniature 

 earthquakes in fact.' I question very much whether gas has anything 

 to do with these bumps, etc., even in coal-mines, but that they act 

 upon the gas is exceedingly probable. The phenomena are certainly 

 often very striking, and would seem to be worthy of much more 

 attention than they have received. With Mr. Strahan's last paragraph 

 I quite agree. W. S. Gresley, F.G.S. 



OvEKSEAL, 8 Sept. 1887. 



THE DATE OF THE ICE AGE. 



Sir, — Some time ago you inserted a letter of mine in which I 

 contended that a high eccentricity of the earth's orbit and winter 

 aphelion would not produce all the effects which Dr. Croll assigned 

 to them. I venture now to give some reasons for thinking that the 

 Glacial Period did not occur so long ago as Dr. CroU's theory 

 supposes. His principal maximum of eccentricity took place 800,000 

 years ago, while the last large maximum was about 210,000 years 

 ago. Can the Ice Age have been as remote as this ? 



I have just returned from a visit to the Lake District, the glacial 

 phenomena of which have been very fully described by Mr. J. 

 Clifton Ward. The traces of ice-action along the sides of the 

 mountains bordering the Valley of Borrowdale are remarkably 

 numerous and well-defined. The sides of these mountains are 

 usually steep and pretty bare, and the rainfall of the district is 

 enormous. At Seathwaite, situated at the head of the valley. Sir 

 John Herschel gives the annual rainfall at 141 inches, and Eamsay 

 at 113 inches. No doubt the rocks are hard volcanic rocks which 

 would stand a good deal of wear ; but would the ice-markings be as 



^ I recollect seeing it stated in a newspaper a few years ago that the wife of the 

 colliery manager was disloged from her seat in the house in Nottinghamshire at the 

 same moment that a very heavy " bump " occurred in the workings of the colliery 

 below, which at the time was, by some, attributed to an earthquake. 



